Police said the bicyclist, David LeClair, 23, of Watertown, Mass., was killed instantly when hit by a tractor-trailer.

LeClair was riding with a group of friends as part of the Trek Across Maine.

LeClair apparently was struck by the rear portion of the tractor-trailer as it passed him, according to Maine State Police.

Friends he was riding with stopped to render assistance and called police with a description of the truck, which police said did not stop.

Bob Moulton lives across the street from the crash site. He said he couldn't see the cyclist's body on the road at first because so many people were around the victim.

"I heard the screaming and hollering from downstairs," said Moulton. "One of the bikers yelled at me and wanted to know what town they were in and what street they were on."

A truck of a similar description was stopped in Rumford by police a short time later. The driver is being interviewed and the truck is being examined by a team of troopers who are now investigating the crash.

The truck driver told state police he didn't stop because he didn't feel or notice anything at all. He said he passed a lot of bikers.

The Trek Across Maine began Friday morning at nearby Sunday River in Newry.

Many of the cyclists hadn't heard about the accident until they reached the end of Day 1 of the three-day ride.

"Our thoughts go out to the people affected, and it's a terrible tragedy. We hope the best for everyone," said cyclist Rick Leonard.

WMTW News 8's Jim Keithley said organizers told him the Trek Across Maine will continue.

Two thousand cyclists are taking part in the event.

Jeff Seyler, CEO of the American Lung Association of the Northeast, issued a statement about the accident.

"It is with deepest sadness that the American Lung Association of the Northeast reports the passing of a member of our Trek family at our annual Trek Across Maine today. The accident occurred this morning in Hanover, Maine. All of us at the American Lung Association express our profound sadness at this tragic loss of life and offer our deepest condolences to the family. With heavy hearts, the Trek is continuing."

Athenahealth spokeswoman Holly Spring said LeClair was an employee and was part of a more than 150-member team from the company taking part in the trek.

LeClair had been working at Athenahealth for two years.

Spring said some members of the team were returning home to Massachusetts, while some decided to continue the trek.

Spring said the entire company is heartbroken and is mourning LeClair's death.

LeClair was also a graduate of Bentley University.

Vice President of Student Affairs Andrew Shepardson issued the following statement:

"Our community is deeply saddened to learn about the loss of Bentley alumnus David LeClair. David graduated from Bentley University in 2011 with a Bachelor of Science in Management. He was an honors student, a leader on campus and an outstanding young man whose impact on our community will be felt for years to come. Our thoughts and prayers are with his entire family, including his sister who is a rising senior at Bentley University."